Single-chain antibody and application thereof for specifically detecting parallel g-quadruplex

Provided are a single-chain antibody and an application thereof for specifically detecting a parallel G-quadruplex. A DNA sequence encoding the single-chain antibody is shown in SEQ ID NO:1. The DNA sequence is transcribed and translated into the single-chain antibody fragment that is capable of specifically recognizing a G-quadruplex structure in a parallel conformation, achieving differentiation of the G-quadruplex structure in the parallel conformation and other secondary structures. A parallel G-quadruplex DNA can be detected in vitro using an enzyme-linked immunosorbent assay.